Packaged leds with phosphor films, and associated systems and methods

ABSTRACT

Packaged LEDs with phosphor films, and associated systems and methods are disclosed. A system in accordance with a particular embodiment of the disclosure includes a support member having a support member bond site, an LED carried by the support member and having an LED bond site, and a wire bond electrically connected between the support member bond site and the LED bond site. The system can further include a phosphor film carried by the LED and the support member, the phosphor film being positioned to receive light from the LED at a first wavelength and emit light at a second wavelength different than the first. The phosphor film can be positioned in direct contact with the wire bond at the LED bond site.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is continuation of U.S. patent application Ser. No.15/464,596, filed Mar. 21, 2017, which is a divisional of U.S. patentapplication Ser. No. 12/819,795, filed Jun. 21, 2010, each of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure is directed generally to packaged light emittingdiodes (LEDs) with phosphor films, and associated systems and methods.

BACKGROUND

LEDs are increasingly in demand for many purposes because such devicesefficiently produce high-intensity, high-quality light. For example,mobile phones, personal digital assistants, digital cameras, MP3players, and other portable devices use LEDs or other solid statelighting devices to produce white light for background illumination.LEDs may also be used in applications other than electronic devices, forexample, in ceiling panels, desk lamps, refrigerator lights, tablelamps, streets lights, automobile headlights, and other instances inwhich lighting is necessary or desirable.

One challenge associated with producing LEDs is containing productioncosts in a manner that allows LEDs to be priced competitively with othermore conventional lighting sources. Because a significant fraction ofthe cost of an LED is attributed to the process for making the LED,manufacturers have attempted to reduce processing costs. One aspect ofthe processing costs relates to the use of phosphor in a packaged LEDsystem. In particular, typical LEDs emit blue light, while manyapplications require or at least benefit from softer colored or whitelight. Accordingly, manufacturers coat such LEDs with a phosphor thatabsorbs a portion of the emitted blue light and re-emits the light asyellow light, producing a composite light emission that is white or atleast approximately white.

Existing processes for providing a phosphor region in the emitted lightpath of an LED can add significantly to the cost of the LED. One suchprocess includes placing the LED in a cavity or recess of a supportingsubstrate, and then filling the cavity with phosphor. Another approachincludes placing the LED on a flat substrate and then building a damaround the LED and filling the interior region with phosphor. Stillanother approach includes depositing a phosphor layer directly on theLED die and then removing part of the phosphor to expose the underlyingbond pads, thus allowing electrical connections to be made to the die.While the foregoing processes have resulted in LEDs that producesuitable light emission characteristics, they all contribute to the costof the LED. Accordingly, there remains a need in the industry for animproved, low-cost processing technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic, cross-sectional side view of componentsof an LED system configured in accordance with an embodiment of thedisclosure.

FIG. 2 is a partially schematic, cross-sectional side view of thecomponents shown in FIG. 1, joined to form a package in accordance withan embodiment of the disclosure.

FIG. 3A is a flow diagram illustrating a process for forming a phosphorfilm in accordance with an embodiment of the disclosure.

FIG. 3B is a flow diagram illustrating a process for forming amulti-layer phosphor film in accordance with another embodiment of thedisclosure.

FIG. 4 is a partially schematic, cross-sectional exploded side view of apackage having a multi-layer phosphor film in accordance with anembodiment of the disclosure.

FIG. 5 is a partially schematic illustration of multiple methods forforming LED packages in accordance with further embodiments of thedisclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed generally to packagedlight emitting diodes (LEDs) with phosphor films, and associated systemsand methods. Specific details of several embodiments of the disclosureare described below with reference to particular LEDs to provide athorough understanding of these embodiments. In other embodiments,aspects of the present disclosure can be used in conjunction with LEDshaving other configurations. Several details describing structures orprocesses that are well-known and often associated with LEDs, but thatmay unnecessarily obscure some significant aspects of the presentdisclosure are not set forth in the following description for purposesof clarity. Moreover, although the following disclosure sets forthseveral embodiments of different aspects of the invention, several otherembodiments can have different configurations, different components,and/or different processes or steps than those described in thissection. Accordingly, the invention may have other embodiments withadditional elements, and/or without several of the elements describedbelow with reference to FIGS. 1-5.

FIG. 1 is a partially schematic, cross-sectional side view of an LEDsystem 100 that includes components that are combined to form a package101 in accordance with an embodiment of the disclosure. These componentscan include a support member 140 carrying an LED 130, and a phosphorfilm 110 optionally supported by a carrier 120. The phosphor film 110 isconformal, and is attached to the LED 130 and the support member 140after the LED 130 is connected to the support member 140 with wire bonds104. Further details of this arrangement and associated processes aredescribed below.

In a particular embodiment shown in FIG. 1, the support member 140 isformed from a ceramic or other suitable substrate material, and has afirst (e.g., upwardly facing) surface 143 a and a second (e.g.,downwardly facing) surface 143 b. Each support member 140 furtherincludes first and second support member bond sites 141 a, 141 b (e.g.,bond pads) that provide for electrical communication to and/or from theLED 130. Accordingly, each of the support member bond sites 141 a, 141 bis connected to corresponding package bond site 102 a, 102 b by acorresponding via 142 or other electrically conductive structure. Thefirst and second packages bond sites 102 a, 102 b are accessible fromoutside the package 101 to facilitate physical and electricalconnections between the package 101 and external devices (not shown inFIG. 1).

The support member 140 carries the LED 130, e.g., at the first supportmember surface 143 a. The LED 130 can include a first LED bond site 131a and a second LED bond site 131 b. The second LED bond site 131 b canface toward and be electrically connected directly to the second supportmember bond site 141 b. In another embodiment, the second LED bond site131 b can face away from the second support member bond site 141 b, andcan be connected to the second support member bond site 141 b with awire bond. In either embodiment, the first LED bond site 131 a can beelectrically connected to the first support member bond site 141 a witha wire bond 104. In a particular aspect of an embodiment shown in FIG.1, the package 101 can also include an electrostatic discharge (ESD) die103 that provides protection for the LED 130 and that is alsoelectrically connected to the first support member bond site 141 a witha wire bond 104, and to the second support member bond site 141 b with asuitable backside surface-to-surface connection. In other embodiments,the ESD die 103 can be omitted.

In an embodiment shown in FIG. 1, the LED 130 has an upwardly facingactive surface 132 through which light (e.g., blue light) is emitted.The phosphor film 110 is positioned over the active surface 132 to alterthe characteristics of the light directed away from the package 101.Accordingly, the phosphor film 110 can include a matrix material 111having a distribution of phosphor elements 112. The phosphor elements112 receive light from the LED 130 and emit the light at a differentwavelength, for example, to produce a composite emitted light that iswhite rather than blue.

In a particular embodiment, the phosphor film 110 is formed from aself-supporting, shape-retaining yet pliant or conformable material. Forexample, the matrix material 111 of the phosphor film 110 can include apartially cured (e.g., b-stage) epoxy material that has enough strengthto be handled when in film form, but which can conform to the LED andassociated features when heated. During processing, the phosphor film110 is brought into contact with the LED 130 and the support member 140,as indicated by arrows C, and heated to form an assembled unit describedlater with reference to FIG. 2. The matrix material 111 can soften dueto the heat, allowing the phosphor film 110 to conform to the LED 130and to the wire bonds 104 that connect the LED 130 to the support member140. In a particular embodiment, the matrix material 111 is sufficientlycompliant at elevated temperatures to conform, flow or otherwise deformaround the wire bonds 104, without displacing, distorting, disturbing,or otherwise changing the location and/or shape of the wire bonds 104.Accordingly, the LED 130 can be wire bonded to the support member 140prior to adding the phosphor film 110, without the phosphor film 110disturbing the integrity of the wire bonds 104.

The matrix material 111 is also selected to be at least partially (andin particular embodiments, completely) transparent to radiation emittedby the LED 130 and the film 110. For example, in cases for which the LEDemits blue light and the phosphor elements 112 emit yellow light, thematrix material 111 is selected to be generally transparent to bothwavelengths. In certain embodiments, the film 110 can include multiplephosphor elements 112 with different phosphor elements selected to emitlight at corresponding different wavelengths. In other embodiments, thepackage 101 can include multiple film layers 110, each having phosphorelements 112 that emit light at a corresponding different wavelength. Inany of these embodiments, the matrix material 111 can be selected to beat least partially (and in particular embodiments, completely)transparent to one or more (e.g., all) the emitted wavelengths.

In a particular embodiment, the phosphor film 110 is strong enough towithstand routine microelectronic device handling techniques as astandalone unit. In other embodiments, the phosphor film 110 can beattached to the carrier 120, which can be rigid or semi-rigid so as toprovide additional support to the phosphor film during the manufacturingprocess. Accordingly, the phosphor film 110 can include a first surface113 a facing toward the LED 130 and the support member 140, and a secondsurface 113 b facing opposite from the first surface 113 a and attachedto the carrier 120. The carrier 120 is typically stiffer and/or morerigid than the phosphor film 120 to provide additional support. In aparticular embodiment, the carrier 120 can include a generally flat,generally rigid, and generally transparent material that providessupport to the phosphor film 110 without affecting the transmission oflight away from the LED 130. For example, the carrier 120 can include aflat layer of glass that is transparent to radiation (e.g., light, andin particular embodiments, visible light). In other embodiments, thecarrier 120 can include features that do affect the light emitted by theLED 130. For example, the carrier 120 can include a lens portion 121that redirects light emitted from the LED 130. In another embodiment,the carrier 120 can include additional phosphor elements 112 beyondthose present in the phosphor film 110. If the carrier 120 includesphosphor elements, the concentration of phosphor elements in the carrier120 is generally less than the concentration of phosphor elements 112 inthe phosphor film 110. The carrier 120 can be fixedly attached to thefilm 110, and can form a permanent part of the package 101. In otherembodiments, the carrier can be released from the film 110 after thefilm 110 is attached to the LED 130 and the support member 140.

FIG. 2 illustrates the package 101 after the phosphor film 110 has beenbrought into contact with the LED 130 and the substrate 140. During themanufacturing process, heat 105 is applied to the elements of thepackage 101, allowing the phosphor film 110 to soften and conform to thewire bonds 104, the LED 130, the ESD die 103 (if present), and/or otherfeatures that may project from or be recessed from the first surface 143a of the substrate 140. Accordingly, the phosphor film 110 cancompletely surround, encapsulate, and/or otherwise accommodate the wirebonds 104 at the first LED bond site 131 a, the first support memberbond site 141 a, and/or locations of the wire bond 104 between the twobond sites 113 a, 141 a. The entire package 101 can then be fully curedto harden the phosphor film 110 in the shape and position shown in FIG.2, with the phosphor film 110 adhered to the LED 130 and the substrate140.

FIG. 3A is a schematic block diagram illustrating a process 300 a forforming a phosphor film 110 in accordance with an embodiment of thedisclosure. In one aspect of this embodiment, a matrix material 111(e.g., a softened, liquid, or otherwise flowable or malleable epoxy orother material) is combined with phosphor elements 112 to form a mixture114. The phosphor elements 112 can be uniformly distributed in thematrix material 111. Thereafter, the mixture 114 can be shaped orotherwise manipulated to produce the phosphor film 110 in accordancewith any of a variety of suitable techniques. Such techniques caninclude a spin-on process, a squeegee process, or another process thatproduces a phosphor film 110 having a uniform thickness. The phosphorfilm 110 can then be partially cured prior to being applied to the LED,as described above with reference to FIGS. 1 and 2.

FIG. 3B illustrates another process 300 b for forming a phosphor film310 in accordance with multiple further embodiments. In theseembodiments, the phosphor elements need not be distributed uniformly inthe matrix material. For example, the process can include forming amatrix film layer 115 a from the matrix material 111, using any of thefilm-forming processes described above. The matrix material 111 canaccordingly have the adhesive and pliancy characteristics describedabove. The phosphor elements can then be disposed directly on the matrixfilm layer 115 a using a phosphor deposition process (shown in block116). In an alternative embodiment, the phosphor elements can themselvesbe formed into a separate, phosphor film layer 115 b, also using any ofthe foregoing techniques described above. In this embodiment, thephosphor film layer 115 b is then attached to the matrix film layer 115a. In either of the foregoing embodiments, the result is a multi-layerphosphor film 310 having a nonuniform distribution of phosphor elements.

FIG. 4 is a partially schematic, exploded elevation view of a package401 having a multi-layer phosphor film 310, e.g., formed using any ofthe techniques described above with reference to FIG. 3B. Themulti-layer phosphor film 310 can include the first layer 115 a formedfrom a matrix material, and the second layer 115 b formed from phosphorelements 112. As discussed above, the phosphor elements 112 and/or setsof phosphor elements 112 can be selected to emit radiation at one ormore than one wavelength. The phosphor elements 112 are concentrated ina region that is directly adjacent to the LED 130. As discussed abovewith reference to FIG. 1, the multi-layer phosphor film 310 can be selfsupporting or not self supporting, and in either embodiment, can includea carrier 420 to provide additional support. In an embodiment shown inFIG. 4, the carrier 420 does not include a lens portion. In otherembodiments, the carrier 420 can include a lens portion, e.g., similarto the lens portion 121 described above with reference to FIG. 1.

FIG. 5 is a partially schematic illustration of different techniques forapplying the phosphor film to the LED in accordance with severalembodiments of the disclosure. In a particular embodiment, the phosphorfilm 510 can be formed directly on a carrier wafer 520 and can be sizedto provide coverage for a multitude of LEDs. In one aspect of thisembodiment, the carrier wafer 520 and the film 510 can be diced togetherto form film elements 516. Individual film elements 516 are thenindividually placed on corresponding substrates 140 (one of which isshown in FIG. 5) using a conventional pick-and-place process. In anotherembodiment, the wafer carrier 520 and the film 510 can be diced afterbeing attached to the corresponding LEDs. For example, the wafer carrier520 and the associated film 510 can be attached directly to an LED wafer133, having LEDs that are already wire bonded to pre-patterned orotherwise formed electrical lines in the LED wafer 133 itself. After thefilm 510 and the carrier wafer 520 have been attached to the LED wafer133, the entire assembly can be diced or singulated to produceindividual packages, e.g., having a configuration similar to that shownin FIG. 2.

In another embodiment, different phosphor films (e.g., phosphor filmshaving different concentrations, distributions and/or types of phosphorelements) can be applied to singulated LEDs to account for differencesin the output (e.g., color of the emitted light) produced by the LEDs.For example, individual LEDs typically have somewhat different emittedlight characteristics due to variations in the associated manufacturingprocesses and are accordingly “binned” so that LEDs with similar lightcharacteristics are grouped together. LEDs from different bins canreceive phosphor films that have different phosphor characteristics todifferentially adjust the light output of the resulting package. Usingthis technique, LEDs from different bins can be packaged so as toproduce the same or nearly the same light output, and/or LEDs within abin can be packaged to conform to other LEDs within the bin. Anadvantage of this technique is that it can reduce or eliminate thenumber of bins used to categorize LEDs, and/or improve the uniformity ofLEDs within a bin.

One feature of at least some embodiments described above with referenceto FIGS. 1-5 is that they can include a pre-formed, phosphor-containingfilm that is placed on a corresponding LED (at the wafer level or theindividual die level) after the LED has been wire bonded to a suitablesupport structure. Because the phosphor elements are carried by a film,they need not be deposited directly on the LED in a liquid or otherform. As a result, the support member need not include a cavity, recess,dam, or other containment feature that contains and/or confines thephosphor elements. In addition, it is expected that in at least someembodiments, the distribution of phosphor elements, once applied to theLED, will be more uniform than the distribution obtained withconventional techniques.

Another advantage of embodiments of the foregoing process is that,because the film is compliant, it can conform to the shape of theunderlying wire bonds, without further processing. In particular, theconformal nature of the film can eliminate the need to cut grooves orrecesses in the film to accommodate the wire bonds. Accordingly, theprocess can require fewer steps than are used in some conventionaltechniques. Embodiments of the process can also eliminate the need tolay down a separate layer that covers the wire bonds, prior to disposingthe phosphor elements on the LED, which is a process used in otherconventional techniques. This feature allows the phosphor in the film110 to be positioned directly adjacent to the LED 130, e.g., directlyadjacent to the active surface 132. Still further, the phosphor elementscan be added to the film prior to engaging a film with the LEDs. Thisfeature allows the film to be manufactured entirely separately from theLED dies, e.g., in parallel with manufacturing and processing the dies.This arrangement can reduce the flow time required to package a die andcan allow the dies and films to be formed or stockpiled separately,which reduces the likelihood for bottlenecks to form in the overallmanufacturing process. The foregoing features, alone or in combination,can reduce the time and expense associated with packaging the die and,accordingly, can reduce the cost of the resulting die package.

From the foregoing, it will be appreciated that specific embodiments ofthe disclosure have been described herein for purposes of illustration,but that various modifications may be made without deviating from thedisclosure. For example, the matrix material can include othercompositions (e.g., other than epoxy), that also provide support for thephosphor elements, and that have adhesive characteristics to facilitatebonding to the LED and/or the support member. Such materials caninclude, but are not limited to, solid state, partially cured thermosetadhesive materials, of which b-stage epoxy is one example. The LEDs canhave shapes, sizes, and/or other characteristics different than thoseshown in the Figures. Certain aspects of the disclosure described in thecontext of particular embodiments may be combined or eliminated in otherembodiments. For example, the carrier 120 shown in FIG. 1 may beeliminated in some embodiments, and may be combined with the phosphorfilm shown in FIG. 4 in other embodiments. Further, while advantagesassociated with certain embodiments have been described in the contextof those embodiments, other embodiments may also exhibit suchadvantages. Not all embodiments need necessarily exhibit such advantagesto fall within the scope of the present disclosure. Accordingly, thedisclosure and associated technology can encompass other embodiments notexpressly shown or described herein.

What is claimed is:
 1. A method for manufacturing an LED assembly,comprising: mounting an LED to a support member; electrically connectingthe LED to the support member with a wire bond; heating aself-supporting pre-shaped phosphor film; applying the heatedself-supporting pre-shaped phosphor film to the wire bond, the LED andthe support member such that the phosphor film deforms around andcompletely surrounds the wire bond without changing a location and/orshape of the wire bond; and curing the phosphor film.
 2. The method ofclaim 1, wherein the phosphor film includes a first layer of matrixmaterial, and a second layer of phosphor elements disposed insurface-to-surface contact with the first layer of matrix material. 3.The method of claim 2, wherein the matrix material is at least partiallytransparent to radiation emitted by the LED.
 4. The method of claim 1,wherein during application, the heated self-supporting pre-shapedphosphor film is attached to a carrier having a stiffness greater than astiffness of the phosphor film.
 5. The method of claim 1, wherein thecarrier includes a lens portion opposite the phosphor film from the LED.6. The method of claim 1, wherein the carrier includes a generally flatmaterial that is transparent to radiation emitted by the LED.
 7. Themethod of claim 1, wherein the carrier includes additional phosphorelements at a lower concentration than a concentration of phosphorelements in the phosphor film.
 8. The method of claim 1, furthercomprising forming the phosphor film by: mixing phosphor elements with amatrix material; and partially curing the matrix material.
 9. The methodof claim 1, wherein the LED is a first LED having a first outputcharacteristic, the support member is a first support member, the wirebond is a first wire bond and the phosphor film is a first phosphor filmhaving first phosphor characteristics, and wherein the method furthercomprises: mounting a second LED to a second support member, the secondLED having a second output characteristic different than the first;electrically connecting the second LED to the second support member witha second wire bond; heating a second self-supporting pre-shaped phosphorfilm having a second phosphor characteristic different than the firstphosphor characteristic to at least partially compensate for thedifference between the first output characteristic and the second outputcharacteristic; applying the second heated self-supporting pre-shapedphosphor film to the second wire bond, the second LED and the secondsupport member such that the second phosphor film deforms around andcompletely surrounds the second wire bond without changing a locationand/or shape of the second wire bond; and curing the second phosphorfilm.
 10. The method of claim 9, wherein the first output characteristicis a first color characteristic and wherein the second outputcharacteristic is a second color characteristic different than the firstcolor characteristic.
 11. The method of claim 10, wherein the firstcolor characteristic is a first wavelength and the second colorcharacteristic is a second wavelength different than the firstwavelength.
 12. A method for manufacturing a plurality of LEDassemblies, comprising: mounting a plurality of LEDs to a wafer;electrically connecting the plurality of LED to the wafer with acorresponding plurality of wire bonds; heating a self-supportingpre-shaped phosphor film; applying the heated self-supporting pre-shapedphosphor film to the plurality of wire bonds, the plurality of LEDs andthe wafer such that the phosphor film deforms around and completelysurrounds each of the plurality of wire bonds without changing alocation and/or shape of the plurality of wire bonds; and curing thephosphor film.
 13. The method of claim 12, further comprisingsingulating the wafer to separate the plurality of LED assemblies fromone another.
 14. The method of claim 12, wherein the phosphor filmincludes a first layer of matrix material, and a second layer ofphosphor elements disposed in surface-to-surface contact with the firstlayer of matrix material.
 15. The method of claim 14, wherein the matrixmaterial is at least partially transparent to radiation emitted by theplurality of LEDs.
 16. The method of claim 12, wherein duringapplication, the heated self-supporting pre-shaped phosphor film isattached to a carrier having a stiffness greater than a stiffness of thephosphor film.
 17. The method of claim 12, wherein the carrier includesa plurality of lens portions opposite the phosphor film from andcorresponding to the plurality of LEDs.
 18. The method of claim 12,wherein the carrier includes a generally flat material that istransparent to radiation emitted by the plurality of LEDs.
 19. Themethod of claim 12, wherein the carrier includes additional phosphorelements at a lower concentration than a concentration of phosphorelements in the phosphor film.
 20. The method of claim 12, furthercomprising forming the phosphor film by: mixing phosphor elements with amatrix material; and partially curing the matrix material.